How much salt to add to a saltwater pool
A salt chlorine generator needs the right salinity to work. Here is the simple math for how many pounds of salt to add.
Safety: dosing figures are estimates. Follow the product label, add one chemical at a time, never mix pool chemicals, add chemical to water (never water to chemical), keep chemicals away from children, and re-test before swimming. Add about ¾ of a dose, re-test, then top up. Not a substitute for professional pool service.
Salt is a dissolved solid measured in parts per million (ppm). To raise salinity you add pounds of salt; to compute how many, you only need three numbers: your pool volume in gallons, your current reading, and your target.
The formula
Because water weighs 8.34 lb per US gallon and ppm means “milligrams per liter” — or, in these units, parts per million by weight — the salt to add is:
pounds of salt = gallons × (target ppm − current ppm) × 8.34 × 10⁻⁶
The 8.34 × 10⁻⁶ is simply 8.34 lb/gal divided by one million. In words: every 1 ppm rise needs 8.34 millionths of a pound of salt per gallon.
Worked example
10,000-gallon pool, going from 0 to 3,200 ppm:
10,000 × 3,200 × 8.34 × 10⁻⁶ = 266.9 lb — about seven 40-lb bags.
3,200 ppm is a common target for salt chlorine generators, but check your unit’s manual and set the target it asks for. A useful rule of thumb falls straight out of the formula: raising a 10,000-gallon pool by 1,000 ppm takes 10,000 × 1,000 × 8.34 × 10⁻⁶ = 83.4 lb. Scale that by your pool size and the ppm gap you actually need.
Salt chart (pounds to add)
Pounds of pool salt to raise salinity by a given amount:
| Pool (gal) | +500 ppm | +1,000 ppm | +1,500 ppm |
|---|---|---|---|
| 10,000 | 41.7 lb | 83.4 lb | 125.1 lb |
| 15,000 | 62.6 lb | 125.1 lb | 187.7 lb |
| 20,000 | 83.4 lb | 166.8 lb | 250.2 lb |
| 25,000 | 104.3 lb | 208.5 lb | 312.8 lb |
The full version, including a “from zero to 3,200 ppm” column, is on the salt chart.
How to add it safely and accurately
Test first with fresh salt strips or a digital meter, and trust your generator’s own display as a second opinion. Add salt with the pump running, brush it across the floor so it does not pile up, and give it a full circulation cycle (often 24 hours) to dissolve before you re-test. If you are close to target, add about three-quarters of the calculated amount, re-test, and top up — it is far easier to add more salt than to remove it. The only way to lower salinity is to drain and dilute with fresh water.
Use pure pool-grade salt (sodium chloride), not rock salt with anti-caking additives or iodized table salt. Salt is not consumed by the generator; you top it up mainly to replace what is lost to splash-out, backwashing and rain overflow, so once a pool is set it usually needs only occasional adjustment.
Reading salinity accurately
Good dosing starts with a good reading. You have three ways to measure salinity, and they do not always agree:
- Test strips are quick and cheap but the least precise; use fresh strips and read them in good light.
- A digital salinity meter is the most accurate for a spot check, provided you calibrate it and account for water temperature, which shifts the reading.
- Your generator’s own display is a useful second opinion, but it is really measuring conductivity and can drift as the cell ages or scales up.
Sample the water elbow-deep, away from returns and the skimmer, after the pump has been running so the salt is fully mixed. If the generator and your test disagree by more than a little, trust a freshly calibrated meter and consider cleaning the generator cell.
Why salinity drifts over a season
Salt is not consumed by the generator, yet the reading still falls over time. The culprits are all water changes: splash-out, backwashing the filter, draining after heavy rain, and topping up with fresh water all dilute or remove salt. Heavy rain can briefly lower the reading; evaporation, which removes water but leaves the salt behind, nudges it up. Because the losses are gradual, an established salt pool usually needs only a small top-up now and then rather than another full charge — test monthly in season and add the modest amount the calculation shows.
The bottom line
Salt dosing is one of the simplest calculations in pool care: pounds equal gallons times the ppm gap times 8.34 millionths. Get an accurate volume, test your current salinity with fresh strips or a calibrated meter, and add pure pool salt for the difference — always the smaller side of your estimate first, since you can add more but cannot easily take it out. Brush it around with the pump running, give it a full circulation cycle to dissolve, and re-test before topping up. After the initial charge, a salt pool loses salinity only slowly to splash-out, backwashing and dilution, so most of the season you are making small adjustments rather than big additions. Keep it in your generator’s recommended range and it will produce chlorine reliably all summer.
Get an exact figure for your readings with the salt calculator, plan a fresh conversion with the salt conversion tool, or lower a too-salty pool with the salinity tool.